1. Field of the Invention
The present invention relates to a substrate holding apparatus for holding a semiconductor substrate in semiconductor processing equipment and, more particularly, to a structure of a susceptor for holding a substrate in plasma CVD equipment.
2. Description of the Related Art
Conventional susceptors used in plasma CVD equipment comprises an electrode made of aluminum or aluminum alloy which has been anodized on the surface thereof as disclosed in U.S. Pat. No. 5,039,388. This is to provide a susceptor with resistance to fluorine in order to prevent it from generating a contaminant as a result of a reaction with active species in fluorine during plasma etching using a gas including fluorine atoms to clean the interior of the reaction chamber. However, cracks can occur on the surface of a conventional anodized susceptor in a plasmatic environment at about 400.degree. C., and this has resulted in a problem in that fluorine based active species penetrate into the cracks and react with aluminum to generate a contaminant.
Under such circumstances, susceptors have been developed which are formed by a ceramic material having a high frequency electrode embedded therein. This approach takes advantage of the fact that ceramic materials such as aluminum nitride are resistant to fluorine based active species and are excellent in thermal conductivity. However, early susceptors of this type had poor thermal efficiency and were not preferable in process stability because semiconductor substrates on such susceptors were heated by radiation heat from a lamp in a room separated from the vacuum reaction chamber.
The next generation of this type susceptors were those which were manufactured by embedding both of an electrode and a heater wire within aluminum nitride to provide a heating portion and a mount portion (electrode portion) in the same structure. Such integration solves the problem of heat efficiency because a semiconductor substrate can be heated directly instead of being indirectly heated as described above.
While the interior of a reaction chamber of plasma CVD equipment is cleaned by means of plasma etching using a gas including fluorine atoms as described above, parts such as a shower head which are technically difficult to manufacture from ceramic materials are manufactured from aluminum alloys and the like as in the prior art. As a result, corrosion is caused by fluorine active species to generate a contaminant. Such a contaminant sticks to the inner wall of a reaction chamber and especially to the surface of a susceptor. Thus, even if the interior of a reaction chamber is cleaned through plasma etching, a new contaminant sticks to the surface of the susceptor. In order to eliminate such a contaminant, the susceptor must be periodically removed for cleaning and maintenance. In this case, since it takes a very long time to remove and clean such an integrated susceptor, the apparatus must be stopped for a long time. This results in the problem of reduced productivity. A problem arises also from the viewpoint of cost in that a susceptor made of aluminum nitride having an integrated structure is quite expensive.
It is therefore an object of the invention to provide a substrate holding apparatus which is highly resistant to fluorine based active species and free from the risk of contamination caused by impurities.
It is another object of the invention to provide a substrate holding apparatus which can be easily replaced and cleaned, thereby improving productivity.
It is still another object of the invention to provide a substrate holding apparatus at a low cost, thereby reducing the operating cost of such an apparatus.